太阳风流界面的成因

ORIGIN OF SOLAR WIND STREAM INTERFACES

在日心距离１ＡＵ处的高速流的前沿部位，经常观测到厚度≈１０＾４ｋｍ的流界面（ｓｔｒｅａｍｉｎｔｅｒｆａｃｅ：）：跨过它密度陡降，温度陡增，风速上升，气压和磁场几乎连续。本文从日心距离０．３ＡＵ处一典型高速流的方位剖面出发，采用二维定态ＭＨＤ模型，研究它在日球赤道面内随日心距离的演化。结果表明，流界面系高速流前沿非线性演化的产物。它先于前、后向激波形成，在日心距离１ＡＵ处得到充分发展。

Observations reveal that stream interfaces of thickness ≈104km frequently appear at 1 AU within the leading edge of high-speed streams,characterized by a steep decrease of density,a steep increase of temperature,an enhancement of solar wind speed,and almost continuous gas pressure and magnetic field.In terms of a two-dimensional steady MHD model this paper studies the evolution of a typical high-speed stream, prescribed at 0.3 AU as a function of the azimuthal angle,with the heliocentric distance in the heliospheric equatorial plane.The results show that the stream interface is an outcome of nonlinear evolution of the leading edge of the high-speed stream.It forms earlier than the forward and reverse shocks,being fully developed at 1 AU,and may extend further to the outer heliosphere as one of the characteristic features within the leading edge of the high-speed stream.